1. Field of the Invention
The present invention relates to an ink jet recording apparatus in which photo-curable ink is used.
2. Description of the Related Art
Generally, in an ink jet recording apparatus, noise during printing is relatively small and the print quality is good, so that it has been widely used.
The ink jet recording apparatus jets fine ink droplets from nozzles of the recording head toward a recording medium such as a paper by using, for example, piezoelectric elements, heater elements or the like, and moves a relative position of the recording head and the recording medium while making ink penetrate the recording medium or fixing ink on the recording medium so as to form an image on the recording medium.
There are, for example, a serial head type and a line head type ink jet recording apparatuses. In the serial head type, a recording head reciprocates on the recording medium and the recording medium is carried in a direction perpendicular to a scanning direction of the recording head for forming an image. In the line head type, a recording head which has a nozzle line having a recording range width for the recording medium is fixed, and an image is formed by carrying the recording medium perpendicular to a width direction of the recording medium.
Recently, in a field of printing on goods or packing material for goods, demand for a small-lot production have been increasing, so that the ink jet method in which a small-lot production can be achieved at low cost in comparison with the method such as a gravure printing method or a flexographic method which needs a plate making has been used.
As is well known, material with less ink absorptivity such as resin or metal is hardly used for goods or packing material for goods.
For enabling the ink to be fixed on the recording medium when such the material with less absoptivity is used as a recording medium, an ink jet recording apparatus of photo curable type in which the photo curable ink with high viscosity is irradiated with light such as ultraviolet-rays (UV-rays) after the ink was jetted and attached to the recording medium to cure and fix the ink on the recording medium has been developed.
Earlier, as the ink jet recording apparatus of the photo curable type, an ink jet recording apparatus of an ultraviolet curable type has been put to practical use, in which radical polymerization ink is used and a great deal of UV-rays is radiated all at once. As a light source, it has been proposed to use a light source which radiates light with directivity such as laser beam or the like (see, for example, Japanese Patent Laid-Open Publication No. 2001-310454 (P.4)). Specifically, as the light source which radiates light with directivity, a semiconductor laser, a light emitting diode or the like is well known.
By using a semiconductor laser or a light emitting diode, a calorific value during irradiation becomes small, so that electric power consumption is lowered. In addition, a light source unit becomes small in comparison with a fluorescent lamp or a high pressure mercury lamp. Moreover, a semiconductor laser or a light emitting diode is good in stability and easy to adjust light quantity.
However, there has been a following problem in the earlier developed technique.
When radical polymerization ink is used, relatively a great deal of UV irradiation is required. Thus, a high-power light source is to be mounted, thereby causing the apparatus to become large and raise the cost of production.
To solve the problem, it is considered to use cationic polymerization ink which has not been put to practical use. However, cationic polymerization ink has a unstable property such as a humidity dependency and a property to cause curing reaction with weak light such as reflection light or the like, so that it is hard to handle and difficult to put into practical use.
For example, degradation of a light source by long-term use lowers lighting intensity to the ink, and decline of lighting intensity is caused by ink mist as the light source gets closer to the recording head by request of miniaturizing the apparatus and the like. Under the circumstances, when the cationic polymerization ink with the above described properties is used, curing failure is likely to occur and it does not reach the stage of practical use.
Especially, when a plurality of light sources are used with respect to each recording head, the lighting intensity which is required for curing reaction is ensured by the plurality of light sources. However, when even only one of the light sources is degraded or affected by the ink mist to lower the light quantity, the lighting intensity which is required for curing reaction cannot be ensured. When the light quantity of a light source is lowered, maintenance is needed to be performed. However, when the plurality of light sources are used as described above, the timings of lowering the light quantity in each light source differ, so that number of maintenances are increased to increase the burden on workers.